1. Field of the Invention
The present invention relates to a frequency-voltage converting circuit outputting a voltage responding to an inputted frequency, and specifically relates to a frequency-voltage converting circuit having an improved response characteristic.
2. Description of the Prior Art
FIG. 1 is a circuit diagram of a conventional frequency-voltage circuit (hereinafter referred to as F-V converting circuit) used for a display monitor. In the figure, V.sub.D is a synchronizing signal, and this synchronizing signal V.sub.D is given to a trigger input pin of a monostable multivibrator 1. The output terminal of the monostable multivibrator 1 is connected to one end of a resistor R, and the other end thereof is grounded through a capacitor C, and the node of the capacitor C and the resistor R becomes an output terminal of an output voltage V.sub.O nearly proportional to the frequency of the synchronizing signal V.sub.D, that is, nearly inversely proportional to the period.
Next, description is made on operation. The pulse width of the inputted synchronizing signal V.sub.D is determined at a constant length by the monostable multivibrator 1. Thereafter, the signal V.sub.D is smoothed by the smoothing capacitor C, and the smoothing resistor R, and thus the output voltage V.sub.O proportional to the frequency of the synchronizing signal can be obtained.
In the conventional F-V converting circuits, the response is slow due to the time constant of the smoothing capacitor C and the smoothing resistor R, and problems of disturbance of screen display and the like until a predetermined voltage is obtained are left unsolved.